Derivatives prepared by reacting polysaccharides with achiral compounds are known. These derivatives have a structure wherein an achiral group is bonded to a stereoregular polymer chain, so that they can discriminate the asymmetry of various racemic modifications when used as column packings for liquid chromatography. However, they are apt to fail in discriminating the asymmetry of some racemic modifications of compounds having complicated structures such as those having two asymmetric centers in the same molecule or those having various functional groups in their asymmetric centers.
The present invention aims at providing a polysaccharide derivative and a separating agent having a higher asymmetry discriminating power, which are prepared by reacting a polysaccharide with a chiral compound to thereby regulate the configurations of both the backbone chain and the side chain.
.beta.-Lactams are important substances as raw materials for the preparation of various drugs including antibiotics. The separation of a .beta.-lactam into respective stereoisomers is essential because the action of such a drug on a living organism is, in many cases, different depending upon the kind of stereoisomer used in the preparation thereof, like in the case of thalidomide [see G. Blaschke, Angew. Chem. Int. Ed. Engl., 19, 13 (1980)].
Known processes for preparing a .beta.-lactam stereoisomer include asymmetric synthesis, diastereomer process and chromatographic process. Among these processes, the chromatographic process has advantages in that a high-purity stereoisomer can be obtained and continuous operation because possible by employing Sorbex techniques. However, none of the columns which have been used for the separation of .beta.-lactam stereoisomers exhibit a sufficiently high separating power and, therefore, the separation of same .beta.-lactams has been impossible as yet.